Significant improvements in both fuel efficiency and performance of an internal combustion engine may be realized by the use of a camless valvetrain and electronic valve actuation. For example, the use of electronic valve actuation may allow control of such variables as valve lift and timing. In engines that utilize a mechanical drivetrain with a camshaft, these two parameters may be fixed at values selected as compromises for many different engine operating conditions. In contrast, the use of variable lift and timing may enable improved power, torque, and fuel economy by allowing these engine parameters to be optimized for current conditions.
Various difficulties have been encountered with the use of electronically actuated valves in an internal combustion engine. For example, hydraulic and magnetic actuators have been proposed. However, each of these solutions may impose high energy and package costs, potentially making implementation difficult. Furthermore, various parameters such as valve lift and landing speed may be difficult to control in current electronically actuated valves. High landing speeds may lead to problems with valve wear and excessive noise.
The inventors herein have realized that the above-described problems may be addressed through the use of an electronically actuated valve assembly for an internal combustion engine, wherein the valve assembly comprises a valve stem, and a plurality of shape memory alloy segments in operative communication with the valve stem, wherein each shape memory alloy segment is individually actuatable, and wherein actuation of different shape memory alloy segments is configured to cause different valve lifts. Such an actuator may occupy less space than hydraulic or electromagnetic actuators, may utilize less power for actuation, and also may provide a greater degree of control over valve lift and landing.